The present invention relates to the separation of solid particles from a liquid suspension. More specifically, it relates to the removal of suspended solids from liquid which has been partially clarified by gravitational separation in a clarifier tank.
The use of clarifier tanks for the gravitational separation of solids from liquids is well known. Such tanks have been used for separating precipitates formed in chemical processes and for a variety of other industrial purposes. One of the most well-known and widely practiced uses of gravitational clarification is the purification of water or liquid waste, such as water from municipal sewage.
Unfortunately, only a portion of the suspended solids contained in water or liquid waste can be effectively removed by gravitational clarification. Water leaving a clarifier will normally contain a significant amount of fine suspended solids. Further treatment to remove suspended solids from such liquid is thus required to obtain liquid of a high purity. Typically, partially clarified liquid is piped to a location remote from the clarifier tank where it is processed in a tube settler, a sand filter or other conventional solids separation device.
Numerous filtration and other devices have been made to separate solids from a suspending liquid. For example, U.S. Pat. No. 3,343,680 to Rice et al. shows a filtration apparatus. Example 4 of that patent describes the use of an upflow filter containing media comprised of materials having a density somewhat less than that of water.
More recent patents, U.S. Pat. No. 3,424,674 to Webber and U.S. Pat. No. 4,115,266 to Ohshima show somewhat related upflow filtration systems containing buoyant media. Each of these prior systems has unique characteristics, but neither is particularly well suited for the purpose of separating suspended solids from partially clarified water or liquid waste which is the effluent of a clarifier tank.
Specifically, the above devices could not be integrally incorporated in a clarification system.
U.S. Pat. No. 4,062,775 to Pielkenrood and U.S. Pat. No. 4,125,467 to Haddad et al. show devices containing multiple contactors which provide large areas of surface on which suspended solids can coalesce. Haddad further shows the use of such material in a Dorr settling pond so that solid separation by gravitational settling and coalescence can take place in a single unit.
Although such devices might be useful for collecting solids and for other purposes, they could not sufficiently separate fine solids from clarified water or liquid waste. Even if a device shown in the Haddad or Pielkenrood patents could be used, a substantial amount of external processing equipment would be required to obtain high purity liquid from water or liquid waste which was partially clarified in a clarifier tank.